The present invention relates to a vane pump and particularly to a vane pump whose suction efficiency and volume efficiency are improved.
FIGS. 11 and 12 show an outline of a vane pump 100 of the background art. FIG. 11 is a longitudinal sectional view of the vane pump 100. FIG. 12 is a view of a front housing in the state seen from the left side in FIG. 11. In a space surrounded by a front housing 101 and a rear housing 102, a side plate 103, a cam ring 104 and a rotor 105 are provided coaxially.
As shown in FIG. 12, a cam face 106 in the oval shape is formed on an inner face of the cam ring 104. Also, the rotor 105 is mounted to a rotating shaft 107 and arranged within the cam ring 104. A plurality of vanes 108 are provided at the rotor 105 so that they protrude in a radial manner from the outer circumferential face of the rotor 105. With rotation of the rotor 105, the tip ends of the vanes 108 are brought into sliding contact with the cam face 106.
A space between the outer circumferential face of the rotor 105 and the vane 108 as well as the cam face 106 is a pump chamber p. The pump chamber P is changed so that its volume is repeatedly expanded/contracted with the rotation of the rotor 105. And at positions matching the volume expansion process of the pump chamber P, suction ports 109, 110 are provided at the corresponding side plate 103 and a rear housing 102, while at positions matching the contraction process, discharge ports 111, 112 are provided at the corresponding side plate 103. Also, on the side of the rear housing 102 opposite to the discharge ports 111, 112, recesses, not shown, for preventing movement of the rotor 105 in the axial direction by discharge pressure are provided at positions opposite to the discharge ports 111, 112.
The suction ports 109, 110 are provided at the positions horizontally opposed to each other with the rotating shaft 107 interposed between them in FIG. 12, and the discharge ports 111, 112 are provided in a pair so that they are vertically opposed to each other with the rotating shaft 107 interposed between them. Also, a working fluid sucked in through an inlet port 113 is sucked into the pump chamber P from the two suction ports 109, 110 through a first branch passage 114 and a second branch passage 115 provided so that they are horizontally branched to two passages in the rear housing 102 arranged in the form to seal the front housing 101 as shown by a two-dotted chain line in FIG. 12.
However, in the vane pump 100 constructed as above, there is a phenomenon that the suction efficiency of the suction port 110 located in the forward rotation direction (arrow direction) of the rotor 105 becomes poor as compared with the suction efficiency of the suction port 109 located in the backward rotation direction of the rotor 105 with the inlet port 113 as a reference.
That is, since the vanes 108 of the rotor 105 rotate in the direction opposite to the working fluid flowing through the first branch passage 114, the suction port 109 can suck the working fluid efficiently, while since the vane 108 of the rotor 105 is rotated in the same direction as the direction where the working fluid in the second branch passage 115 flows, the working fluid flowing through the second branch passage 115 can not be guided into the suction port 110 favorably, and the suction efficiency of the suction port 110 is lowered. By this, particularly at high rotation, there are problems that the amount of the working fluid required for suction becomes larger than that of the working fluid pressed in on the suction port 110 side with poor suction efficiency, cavitations are caused by a negative pressure on the suction port 110 side, and vibration noises are generated.
Therefore, an invention to solve these problems is proposed in Patent Document 1. When features of the invention described in Patent Document 1 are described referring to FIG. 12, the length of the second branch passage 115 is made shorter than the length of the first branch passage 114 so as to reduce fluidity resistance of the second branch passage 115 so that the suction efficiency of the suction port 110 is improved.
[Patent Document 1] Japanese Patent Application Laid-Open No. HEI 8-74750
However, the invention described in Patent Document 1 has the following problems. That is, as shown in FIG. 12, the high-pressure discharge ports 111, 112 are located at positions away from a mounting portion 116 for mounting the rear housing 102 to the front housing 101. Therefore, the rear housing 102 is deformed so that it is separated from the front housing 101 by the pressure of the working fluid, on the axis passing through the high-pressure discharge ports 111, 112, and a clearance between the rear housing 102 and the rotor 105 as well as the vane 108 is widened. Thus, a leakage of the working fluid from the pump chamber P to another pump chamber P is generated through the clearance and as a result, there is a problem that the volume efficiency is deteriorated.
The present invention was made in order to solve the above-mentioned background art, and its object is to provide a hydraulic pump in which a favorable balance of a suction efficiency of two suction ports is ensured and the volume efficiency is improved.
A vane pump according to the present invention is characterized in that a side plate or a rear housing is positioned in the state where a discharge port is brought close to a mounting portion so that a position of a first suction port located in the forward rotation direction of the rotor is brought closer to a suction port than a position of a second suction port located in the backward rotation direction of the rotor with the suction port as reference.
Since a balance between the suction efficiency of the first suction port located in the forward rotation direction of the rotor and the suction efficiency of the second suction port located in the backward rotation direction of the rotor can be maintained and moreover, the discharge port can be provided in the vicinity of the mounting portion for the front housing and the rear housing, the phenomenon that the rear housing 102 is deformed so as to be separated from the front housing 101 by a pressure of the high-pressure working fluid acting on the discharge port is prevented, and a clearance between the rear housing and the rotor as well as the vane is prevented from being widened. As a result, a leakage of the working fluid from the pump chamber to another pump chamber through the clearance is prevented, and the volume efficiency can be improved.